In web development, the viewport refers to the user's visible area of a web page. It represents the portion of the web page that is currently visible to the user in their browser window or on their device screen.

The size of the viewport can vary depending on the device and browser being used. For example, on a desktop computer, the viewport size is typically larger compared to a mobile device such as a smartphone or tablet.

Developers often need to consider the viewport when designing and developing websites to ensure that their content is displayed correctly and optimally across different devices and screen sizes. This practice is known as responsive web design.

Responsive web design involves using CSS media queries and other techniques to adapt the layout and appearance of a website based on the characteristics of the viewport. This allows the website to provide an optimal user experience regardless of the device or screen size.

By understanding and utilizing the viewport, developers can create websites that are more user-friendly and accessible across a wide range of devices and platforms.